Input and output per second (IOPS) or throughput is used as a method for guaranteeing performance of a storage device, etc.
A busy rate of a storage device is an index which indicates how busy the device is. The busy rate is obtained, for example, based on a ratio of a period of time for which an IO request stays in an IO queue. If the busy rate of a storage device is 100 percent (corresponding to “1” if represented as a value not smaller than 0 and not greater than 1), for example, further performance may not be pulled out from the device. If the busy rate of the storage device is 100 percent, IO requests are piled up on the IO queue and IO operations are being carried out, and it may be difficult to enhance IO performance. An IOPS value may be obtained based on the number of accesses (number of IO operations) counted for every block in a unit of time length.
If a storage device is accessed, the busy rate of the storage device may change based on changes of a disk location and a disk area where an IO operation occurs, a ratio between the numbers of read and write instructions, or how IO sizes are distributed, even if the IOPS value does not substantially change. A time length for an overhead operation in case of IO operations occurring in an entire storage area except for data transfer, for example, a length of seek time is longer than a time length for an overhead operation in case of IO operations occurring in part of the storage area except for data transfer, for example, a length of seek time. The busy rate may thereby be higher in the former case than in the latter case even if the IOPS value does not change.
Japanese Laid-open Patent Publication No. 2001-43032 discusses a related art.